Malleolar Referencing Device

ABSTRACT

A medical marker ( 12 ) device for detection by a navigation system in a navigated medical procedure, comprising: a) an image-detectable two-dimensional marker pattern ( 13 ) for detection by an imaging unit of the navigation system;  b) a carrier part ( 14 ) for carrying the marker pattern ( 13 ); c) a positioning part ( 15 ) for positioning the marker device ( 12 ) on an anatomical structure ( 11 ); and d) a support part ( 16 ) for supporting the carrier part ( 14 ) and the positioning part ( 15 ).

The present invention relates to a medical marker device for detection by navigation system in a navigated medical procedure which comprises in particular an image-detectable two-dimensional marker pattern for detection by an imaging unit of the navigation system. Furthermore, the invention also relates to a combination of such a marker device and a navigation system for conducting a navigated medical procedure.

In navigated medical procedures such as knee operations it is often desirable to determine the longitudinal axis of the tibia (i.e. its proximodistal axis). Known methods for doing so rely for example on medical image information in order to determine the positions of landmarks on the tibia from which the position and orientation of the mechanical, in particular proximodistal and/or longitudinal, tibia axis can be determined. The position and orientation of the mechanical axis is defined in particular by the positions of the proximal endpoint of the tibia and the distal endpoint of the tibia. The distal endpoint is commonly determined as approximately the three-dimensional centerpoint between the positions of the medial malleolus and the lateral malleolus.

These image-based methods however may not provide information about the in-situ placement of for example a cutting block for cutting the proximal end of the tibia for example in knee total endoprosthesis implantation. For in-situ determination of the orientation of such a cutting block relative to the proximodistal tibia axis, the state of the art relies on detection of a marker device indicating in particular the positions of the medial and lateral malleolus, respectively, by for example a stereotactic camera of a navigation system which does not have a fixed position relative to the cutting block. This approach is cumbersome since detection of such a marker device is only possible within the field of view of the stereotactic camera.

A problem to be solved by the present invention therefore is to provide a marker device which serves to simplify in-situ determination of the mechanical tibia axis. In particular the present invention seeks to solve line-of-sight problems when determining the orientation of the cutting block in particular relative to the mechanical axis of the tibia.

This problem is solved by the subject-matter of any appended independent claim. Advantages, advantageous features, advantageous embodiments and advantageous aspects of the present invention are disclosed in the following and contained in the subject-matter of the dependent claims. Different advantageous features can be combined in accordance with the invention wherever technically expedient and feasible. Specifically, a feature of one embodiment which has the same or a similar function to another feature of another embodiment can be exchanged with said other feature. A feature of one embodiment which adds an additional function to another embodiment can in particular be added to said other embodiment.

Exemplary Short Description of the Invention

In this section, individual aspects of the present invention are described by way of mere example without limiting the invention to the combination of features described in this section.

In order to solve the aforementioned problem, the invention provides a marker device comprising at least one image-detectable two-dimensional marker pattern which is provided for example on a planar carrier surface of a carrier part. The carrier part is connected to a positioning part, wherein the position of the carrier part relative to the positioning part may be fixed or adjustable. The positioning part is preferably formed to fit substantially flush onto an anatomical structure such as for example a malleolus, and the positioning part is preferably connected to a support part for supporting the carrier part and the positioning part (and therefore also the marker pattern) on an anatomical structure such as the ankle joint. The support part can be formed as a strap arrangement, a forceps, or as a fixation system shaped as a splint or a shoe or comprising a plate-shaped positioning part which is fastened to the anatomical structure with an adhesive foil.

General Description of the Invention

In this section, a general description of the preferred features of the invention is given.

The invention preferably provides a medical marker device for detection by a navigation system in a navigated medical procedure. In the context of this invention, a marker device is understood to be a physical structure which can be detected by a detection unit of a navigation system in order to determine the position of the marker device in a navigation coordinate system. The navigation system preferably comprises a computer which conducts the electronic data processing for determining that position, the computer being operatively coupled to a detection unit such as an imaging unit (for example a digital camera which may be at least one of a still image camera and a digital camera) which is configured to detect the marker device. The position of the marker device can then be determined for example by analysis of the resulting image, in particular by a known image segmentation algorithm, in order to determine the distance between the imaging plane of the imaging unit and the marker device and to determine the orientation of the marker device relative to the imaging plane. As a result, the spatial relationship (in particular at least one of the position and the orientation) between the marker device and the imaging unit can be determined.

In accordance with the invention, the marker device preferably comprises an image-detectable two-dimensional marker pattern which is detected by the imaging unit. The marker pattern is for example a graphical feature, the specific dimensions of which are preferably known to a position-determination algorithm used by the navigation system in order to determine the spatial relationship between the imaging unit and the marker pattern. In particular, the marker pattern is a graphical feature which is capable of producing an image appearance when imaged by the imaging unit which depends on the spatial relationship between the imaging unit and the marker pattern. For example, the size of the image appearance of the marker pattern can be used to determine the distance between the marker pattern and the imaging plane of the imaging unit, and a difference in shape of the image appearance of the marker pattern compared to its known shape (in particular when viewed in a direction perpendicular to a plane in which the marker pattern is arranged, in particular perpendicular to a carrier surface of the carrier part) may be used to determine the orientation of the marker pattern relative to the imaging plane. For example, the marker pattern is embodied by a moiré pattern which changes its visual appearance depending on the perspective from which it is being looked at. Preferably, the marker pattern is designed such that it has a distinguishable appearance for detection in at least one of a video image and a still image taken by the imaging unit.

Preferably, the marker device comprises a carrier part for carrying the marker pattern, in particular the marker pattern is attached to the carrier part. For example, the carrier part is provided with a planar carrier surface which is provided with a marker pattern (for example, the marker pattern may be printed or stuck onto the planar carrier surface). In an alternative embodiment, the carrier part may be embodied by a rod, to the end of which a planar member representing the marker pattern is attached.

Preferably, the marker device comprises a positioning part for positioning the marker device on an anatomical structure. The positioning part is preferably connected to the carrier part in preferably a predetermined (in particular known) and advantageously fixed spatial relationship (in particular fixed position and orientation) relative to the carrier part. Therefore, the spatial relationship (in particular at least one of the position and the orientation) of the marker pattern relative to the positioning part is also predetermined (in particular known) and advantageously fixed. The positioning part is preferably shaped to be positioned substantially flush with the anatomical structure, in particular with a malleolus (in particular of the skin covering a malleolus). For example, the positioning part is cup-shaped so as to fit onto the exterior surface of a malleolus. By positioning the positioning part on a malleolus, the position of the malleolus and therefore a landmark required to determine the distal endpoint of the tibia axis can be determined based on determining the position of the marker pattern.

Preferably, the marker device comprises a support part for supporting the carrier part and the positioning part. In particular, the support part is connected to at least one of the carrier part and the positioning part. Preferably, the spatial relationship (in particular at least one of the position and the orientation) of the positioning part relative to the support part is adjustable. For example, the support part is forceps-shaped (in particular comprises a forceps) wherein a positioning part is provided preferably at the end of each forceps arm and wherein two of the aforementioned two-dimensional marker patterns are provided on the forceps arms in a predetermined and in particular known spatial relationship relative to the positioning parts. In this case, the orientation of the positioning parts and the forceps arms to which the respectively other part is attached is adjustable by changing the opening angle of the forceps. Alternatively, the support part may comprise an arrangement comprising at least one of the set of straps, a shoe and a splint, each one of which is preferably suitable to fasten the marker device to an anatomical structure such as in particular an ankle joint. If the support part is embodied by a shoe-like structure, this shoe-like structure is preferably designed to form-fit to the anatomical structure, in particular to form-fit to a lower thigh, in particular to an ankle joint.

If the support part is embodied by a set of straps, these straps may be at least partly led through for example the positioning part while allowing the straps to move relative to the positioning part. If the support part is shoe-shaped, the carrier part and the positioning part may be designed so that they can slide in a slot formed in the shoe-shaped support part in at least one dimension. Preferably, a second slot is provided in the shoe-shaped structure which allows to move the arrangement of marker pattern, carrier parts and positioning parts in two degrees of freedom (in particular in two translational directions) relative to the support part. Alternatively, the positioning parts may be attached to the shoe-shaped structure via forceps-shaped connecting arms which are attached to the shoe-shaped structure via a ball joint which allows to position two positioning parts and therefore two marker patterns at each end of the forceps-shaped connecting arms on the anatomical structure, in particular on the malleoli.

As can be seen from the above, the marker device preferably comprises two-image-detectable two-dimensional marker patterns and an individual carrier part for each of the marker patterns (i.e. one carrier part per marker pattern) and an individual positioning part for positioning each carrier part (i.e. one positioning part per carrier part). One example for such configuration is the aforementioned marker device in which the support part is embodied by a set of straps or a shoe-shaped structure. Two further embodiments with two marker patterns are described in the following. For example, the carrier part can be embodied by a carrying plate which is placed on the anatomical structure such as a malleolus (in particular, one such plate is positioned on each malleolus of an ankle joint) and fastened to the ankle joint with a support part comprising an adhesive foil which is wound over the ankle joint and the carrying plate. If the marker device comprises two marker patterns, two such carrier plates may be used (one for each marker pattern). A marker pattern is then screwed or pushed into an attachment structure of each of the plate (or plates, respectively) through the adhesive foil. In that case, the carrier part is preferably embodied by a male screw thread or a pin which is located in the attachment part of the plate. Alternatively, the support part may be formed as a splint for the ankle joint having a slot in the proximodistal direction which covers the potential proximodistal positions on the malleoli on each lateral side of the splint, and a carrier part and a positioning part with each a marker pattern attached to the carrier part may be provided in each of the slots so as to be movable in the proximodistal direction.

It is clear from the above that it is preferred that if the marker device comprises two marker patterns (and therefore correspondingly two carrier parts and positioning parts), each one of the positioning parts is adjustable relative to the support part so as to be positioned at different positions. In particular, the position parts can be positioned at each a different position so as to be located at the correct proximal distal position of the medial and lateral malleolus, respectively, which in general are not located in the same horizontal plane of the patient's body. In particular in the embodiment having a support part comprising an adhesive foil and a carrier part being embodied by a carrier plate, the marker pattern, the carrier part, the positioning part and the support part are detachably connectable (in particular connected) to each other.

In a further preferred embodiment, the marker device comprises only one marker pattern. In this embodiment, the support part is embodied by for example a strap to which the positioning part is attached preferably such that it is adjustable with regard to the support part (i.e. the strap, for example along the in particular longitudinal direction of the strap). The carrier part is connected to the support part with a connecting part so that the carrier part is movable in particular in the lateral direction when the support part is fixed to the anatomical structure (in particular to the ankle). The position of the marker pattern is then preferably adjusted by user interaction to define approximately the centre between the positions of the two malleoli on that ankle and therefore to define the distal endpoint of the corresponding tibia. Further preferably, the marker device (in particular the carrier part and/or the connecting part) is brought into predetermined orientation relative to the patient's sagittal or coronal plane.

In a further preferred aspect, the invention is also directed to a combination of a navigation system (which is described above) and the above-described marker device.

In an even further preferred aspect of the invention, the invention also relates to a method of determining a position of the distal endpoint of the mechanical, in particular proximodistal and/or longitudinal, tibia axis based on acquiring information about the position of the marker pattern based on using the above-described marker device. If the marker device comprises two marker patterns, the distal endpoint of the mechanical axis is preferably determined based on acquiring information about the positions of both marker patterns, in particular by determining the position of the distal endpoint to be approximately the three-dimensional centre between the positions of the marker patterns. The invention is then preferably also directed to a program, which when executed on a computer, causes the computer to execute the steps of such a method, and to a computer running such a program.

DESCRIPTION OF THE FIGURES

In this section, the invention is described with reference to the appended Figures, wherein the invention shall not be limited to those features described in relation to and illustrated in the Figures.

FIG. 1 illustrates the geometry of the tibia and the fibula as well as specific landmarks on those two bones;

FIGS. 2a and 2b illustrate a first embodiment of the inventive marker device with a set of straps as a support part;

FIG. 3 illustrates a second embodiment of the inventive marker device with a forceps-shaped support part;

FIGS. 4a to 4c illustrate sub-types of a third embodiment of the inventive marker device with a shoe-shaped support part;

FIGS. 5a to 5c illustrate a fourth embodiment of the invention with an adhesive foil as a support-part;

FIGS. 6a and 6b illustrate a fifth embodiment of the invention with a splint as a support part;

FIG. 7 illustrates a sixth embodiment of the inventive marker device having only one marker pattern.

As shown in FIG. 1, a tibia 9 comprises a medial condylus 6, the tibia tuberosity 7, the anterior crest 8, the lateral condylus 5 and, as a landmark, the medial malleolus 10. The fibula 3 comprises the fibula head 4 and, as a landmark, the lateral malleolus 2. The mechanical, in particular proximodistal and/or longitudinal axis of the tibia 9 is illustrated as a dashed line in FIG. 1. The distal endpoint of the mechanical tibia axis is illustrated as the shaded circle 1 which is shown to lie approximately in the three-dimensional centre between the lateral malleolus 2 and the medial malleolus 10. Specifically, the distal endpoint 1 divides the distance between the lateral malleolus 2 and the medial malleolus 10 approximately in the middle, wherein the distal endpoint 1 lies closer to the medial malleolus 10 than to the lateral malleolus 2.

FIGS. 2a and 2b show a first embodiment of the inventive marker device 12 having two marker patterns 13 a, 13 b which are illustrated as square graphical features positioned on a planer carrier surface of carrier parts 14 a, 14 b, respectively. The carrier parts 14 a, 14 b are connected to positioning parts 15 a, 15 b which can be adjusted in their positioning relative to a set of straps representing the support part 16. The set of straps can be fixed around the ankle 11 so that the positioning parts 15 a, 15 b and therefore the marker patterns 13 a, 13 b have a fixed spatial relationship relative to the malleoli. In particular, the positioning parts 15 a, 15 b are designed such that they can be properly positioned on the malleoli 2, 10 only in a predetermined spatial relationship, and the position of the malleoli can be determined in particular from the position and orientation of the marker patterns 13 a, 13 b relative to an imaging unit (e.g. a digital camera) of a navigation system.

According to FIG. 3, the inventive marker device 12 comprises a support part 16 embodied by a forceps, on the arms of which two marker pattern 13 a, 13 b are fastened in a predetermined spatial relationship relative to the positioning parts 15 a, 15 b (positioning part 15 b not being shown in FIG. 3, but lying symmetrically on the other side of the ankle 11 relative to positioning part 15 a) via carrier parts 14 a, 14 b embodied by connecting reads rods between the forceps arms and the marker pattern 13 a, 13 b.

In FIG. 4a , the marker device comprises a shoe-shaped structure as a support part 16 which may be fitted around the heel so that the positioning parts 15 a, 15 b (the latter not being shown in FIG. 4a ) on the malleoli 2, 10 while being moveable in a slot provided in the shoe-shaped structure in the anteroposterior direction of the ankle joint. In particular the carrier parts 14 a, 14 b are located in the slot, and the marker patterns 13 a, 13 b extend to the exterior of the slot so as to be detectable by the imaging unit. The slots allow moving the carrier parts 14 a, 14 b and therefore the marker patterns 13 a, 13 b in the anteroposterior direction of the ankle 11 as illustrated by the double arrow in FIG. 4 a.

FIG. 4b shows a further development of the marker device 12 illustrated in FIG. 4a in which the shoe-shaped structure (support part) 16 is provided with a second slot, in which a holding part provided with the first slot described with reference to FIG. 4a can be moved additionally in the proximodistal and/or longitudinal direction of the ankle joint 11. Thereby, positioning of the positioning parts 15 a, 15 b on the malleoli 2, 10 is further simplified by allowing moving the positioning parts 15 a, 15 b in two dimensions relative to the support part 16.

In FIG. 4c , the carrier parts 14 a, 14 b are attached to the positioning parts 15 a, 15 b. The positioning parts 15 a, 15 b are connected via connecting arms 20 a, 20 b to a ball joint 17 which is disposed on the front part of the shoe-shaped structure 16 so as to allow three-dimensional movement of the positioning parts 15 a, 15 b (in particular relative to the support part 16) for positioning them on the malleoli 2, 10. The freedom of movement is indicated by the two curved arrows in FIG. 4c .

FIGS. 5a to 5c illustrate a further embodiment of the inventive marker device in which the positioning part 15 is embodied by a positioning plate which preferably has a recess 18 which can be placed over a malleolus 2, 10. For example, one such plate is placed on each malleolus 2, 10 of an ankle joint 11 and fixed in position by wrapping an adhesive foil embodying the support part 16 around the ankle joint 11 and over the positioning part 15 a, 15 b. Marker patterns 13 a, 13 b are then attached to the positioning parts 15 a, 15 b by inserting carrier parts 14 a, 14 b into attachment parts (which comprise e.g. a clip or a screw thread) of the carrier plates through the adhesive foil.

FIGS. 6a and 6b show two perpendicular perspectives of a further embodiment of the marker device having a splint as the support structure 16. The splint is positioned on the ankle joint 11 and is provided with a slot running in the proximodistal and/or longitudinal direction of the ankle joint 11 on both lateral sides of the ankle joint 11. The carrier parts 14 a, 14 b are disposed in the slot so as to be moveable in the slot in the proximodistal and/or longitudinal direction of the ankle joint 11 (indicated by the double arrow in FIG. 6b ), so as to be able to adapt the position of each of the planar markers 13 a, 13 b to the different positions of the two malleoli 2, 10 on the ankle joint 11.

FIG. 7 shows an embodiment of the inventive marker device having only a single marker pattern 13. The carrier part 14 is disposed on a connecting arm 19 which is fastened to the positioning part 15. The positioning part 15 is attached to a strap embodying the support part 16. The carrier part 14 is able to move in the lateral directions of the ankle joint 11 as indicated by the double arrow in FIG. 7. This allows a user to position the marker pattern 13 so that it lies on the mechanical tibia axis and in particular indicates the distal endpoint of this axis.

The present invention provides for example the following advantages:

-   -   Due to the possible proximity of the marker device to the         imaging unit, the risk of interrupting the line-of-sight between         the imaging unit and the marker e.g. due to introduction of         physical objects is reduced.     -   Furthermore, the imaging unit can easily be oriented properly         relative to the marker device, provided the imaging unit is         allowed to change its spatial relationship relative to the         marker device if it is e.g. fastened to a cutting block. 

1. A medical marker device for detection by a navigation system in a navigated medical procedure, comprising: a) an image-detectable two-dimensional marker pattern for detection by an imaging unit of the navigation system; b) a carrier part provided with a planar carrier surface for carrying the marker pattern; c) two positioning parts for positioning the marker device on an anatomical structure, wherein the positioning parts are shaped to be positioned substantially flush with the anatomical structure-; and d) a support part for supporting the carrier part and the positioning part.
 2. The marker device according to the preceding claim 1, wherein the marker pattern is a graphical feature configured to produce an image appearance which depends on the spatial relationship between the imaging unit and the marker pattern.
 3. The marker device according to claim 1, wherein the marker pattern is detectable in at least one of a video image and a still image.
 4. The marker device according to claim 1, wherein the spatial relationship of the marker pattern relative to the positioning part is fixed.
 5. The marker device according to claim 1, wherein the spatial relationship, of the positioning part relative to the support part is adjustable.
 6. The marker device according to claim 1, wherein the support part is designed to form-fit to the anatomical structure.
 7. (canceled)
 8. The marker device according to claim 1, wherein the marker pattern is provided on the carrier surface.
 9. The marker device according to claim 1, wherein the support part is forceps-shaped.
 10. The marker device according to claim 1, wherein the support part comprises an arrangement comprising at least one of a set of straps, a shoe and a splint which is configured to fasten the marker device to a joint.
 11. The marker device according to claim 1, wherein the anatomical structure comprises a malleolus.
 12. The marker device according to claim 1, wherein the support part comprises an adhesive foil.
 13. The marker device according to claim 1, wherein the marker pattern, the carrier part, the positioning part and the support part are detachably connectable with each other.
 14. The marker device according to claim 1, comprising two image-detectable two-dimensional marker patterns for detection by a detection unit of the navigation system and an individual carrier part for each of the marker patterns and an individual positioning part for positioning each carrier part.
 15. A combination of the marker device according to claim 1 and a navigation system for conducting a navigated medical procedure.
 16. The marker device according to claim 4, wherein at least one of the position and the orientation of the marker pattern relative to the positioning part is fixed.
 17. The marker device according to claim 5, wherein at least one of the position and the orientation of the positioning part relative to the support part is adjustable.
 18. The marker device according to claim 6, wherein the support part is shoe-shaped.
 19. The marker device according to claim 9, wherein the support part comprises a forceps. 